1. Field of the Invention
The present invention relates to a gas insulated bus or a gas insulated line (hereinafter collectively referred to as a gas insulated bus when necessary) and a method for removing a particle from the inside of the gas insulated bus.
2. Description of the Related Art
A gas insulated bus (GIB) or a gas insulated line is a component device of a gas insulated substation or a gas insulated transmission line facility and is configured such that a conductor (high-voltage conductor) supported by an insulator is coaxially accommodated in a cylindrical grounded metal container in which insulating gas (typically SF6 gas) is contained. Furthermore, in general, in use, a plurality of gas insulated buses are coupled together in series or coupled to a gas insulated switchgear or a gas insulated transformer, as needed, and thus flanges for coupling are provided at the respective opposite ends of each of the gas insulated buses. Additionally, an insulating spacer with any of various shapes is used as the insulator that supports the high-voltage conductor. For example, a connection conductor to which the high-voltage conductor is connected is allowed to penetrate the center of an insulating spacer formed of an epoxy resin or the like and shaped like a disk or a cone, and the resulting structure is installed in a cylindrical metal container. Alternatively, a columnar post-type insulating spacer or the like is appropriately used as needed.
Such a gas insulated bus has been demanded to satisfy insulation and conductivity performance requirements but also to be smaller in size and more reliable. Here, the insulation performance requirement is the capability of withstanding a voltage that is equal to or higher than, for example, a specified breakdown voltage. However, the insulation performance is significantly degraded when a conductive particle such as metal is present inside the metal container. Thus, strict quality control is performed during manufacturing steps and assembly steps so as to prevent a particle from entering the metal container. On the other hand, the conductivity performance includes satisfying a current capacity requirement and a requirement for an allowable increase in the temperature of the insulating spacer part according to, for example, the JEC standard.
Thus, Reference 1 reports the results of analysis of distribution of an electric field strength near the conical insulating spacer in order to allow a reduction in the size of the gas insulated bus. The Reference 1 reports that the electric field strength in the metal container of a conical outer surface side of the insulating spacer is greater than that in the metal container of a conical inner surface side of the insulating spacer and that the electric field strength in the metal container of the conical outer surface side of the insulating spacer decreases with increasing distance from the insulating spacer. Thus, the Reference 1 proposes that a diameter of the metal container on the conical inner surface side of the insulating spacer be defined to be smaller than that of the metal container on the conical outer surface side of the insulating spacer and that the diameter of the metal container on the conical outer surface side is defined to be small by being defined from a position located at a given distance from the insulating spacer.
On the other hand, a method for conditioning for a particle has been proposed in which a particle trap with a low electric field strength is formed in the metal container and in which before operation, a voltage lower than an operating voltage is applied to a high-voltage conductor in a stepwise fashion to allow a particle to float and accumulate in the particle trap. In particular, Reference 2 proposes that conditioning for a particle be carried out by reducing the insulation performance of insulating gas in order to facilitate motion of the particle.